【作者】 曾植；

【导师】 杨春平； 王建龙；

【作者基本信息】 湖南大学 ， 环境工程， 2008， 硕士

【摘要】 电催化高级氧化技术因其具有处理效率高、操作简便、与环境友好等优点于近年来引起了研究者的广泛注意。从20世纪90年代开始,利用氧在阴极还原生成H₂O₂降解有机污染物是研究的焦点。大多数研究是控制在酸性条件下,外加铁盐或采用铁阳极提供铁离子,由此产生羟自由基（HO·）的“电芬顿”工艺。而本文采用Ti/IrO₂/RuO₂阳极、C/PTFE氧还原阴极,无须外加金属催化剂,充分发挥阳极氧化和阴极还原产物的氧化同时作用处理有机废水。本文采用一种新型电化学体系阴阳极同时作用降解甲基橙,以电还原氧气产生H₂O₂的炭/聚四氟乙烯（C/PTFE）气体扩散电极为阴极,Ti/IrO₂/RuO₂电极为阳极,廉价的涤纶滤膜作为隔膜。研究结果表明:适当的曝气有利于甲基橙的降解;甲基橙脱色率随电流密度的增加而升高;初始pH对甲基橙的脱色效果有一定的影响。在电流密度46 mA/cm²,曝气速度30 mL/s,电解时间60 min时,脱色率可以达到100%,COD平均去除率可达到80%。本研究针对高级氧化技术处理氯酚类污染物有含氯中间产物存在的问题,采用阴极还原脱氯和阴阳极同时氧化相结合的方法对氯酚类污染物进行降解研究。对氯酚类污染物先通过阴极还原脱氯,再通过阳极氧化和阴极还原产物的氧化作用共同处理脱氯后产物使其降解到有机酸阶段,后续生物处理。这一结合充分发挥电化学氧化、还原的优势,既避免了脱氯去毒不完全的问题,又实现了有机物彻底矿化的最终目标。本研究分别采用氢气还原法和甲醛还原法制备了Pd/C催化剂,利用XRD、TEM、XPS及CV对催化剂进行表征,并由催化剂制备成Pd/C气体扩散阴极,在隔膜电解体系中对氯酚类污染物（4-氯酚、2,4-二氯酚和五氯酚钠）进行降解,比较了不同电极体系及不同通气方式下氯酚类污染物的去除效果。结果表明,所制备的Pd/C气体扩散阴极既对氯酚类污染物具有还原脱氯作用（通入H₂时）,又促进O₂还原生成H₂O₂（通入O₂时）。采用先通氢气后通空气的方式对氯酚类污染物有很好的去除效果,氯酚类污染物的转化率和脱氯率均接近100%。因此,Pd/C气体扩散阴极利用电化学还原脱氯和阴阳极同时氧化相结合对氯酚类有机物的降解是可行的。本研究还借助高效液相色谱等现代分析技术,考察了氯酚类污染物的电化学降解行为,从微观和宏观角度探索氯代有机污染物的电化学阴极还原脱氯以及随后的氧化降解机理,为提出一条简单、高效的氯酚类污染物处理工艺建立科学基础。更多还原

【Abstract】 The advanced electrocatalysis oxidation process has attracted a great deal of attention recently, mainly because of its ease of control, amenability to automation, high efficiency and environmental compatibility. Since 1990s, the processes of indirect electrooxidation of organic compounds by hydrogen peroxide （H₂O₂） generated by the reduction of oxygen on the cathode have much promise for treating organic toxicants. Generally, the electro-Fenton process can be realized in the no-diaphragm electrolysis system, where H₂O₂ is produced on the cathode in an acid medium and Fe²⁺ is added or offered by Fe anode. In this thesis, a new electrochemical oxidation system was used to treat the aqueous organic pollutant. It was constructed by a Ti/IrO₂/RuO₂ anode, a self-made carbon/ polytetrafluoroethylene （C/PTFE） O₂-fed cathode and an organic synthetic diaphragm between the anode and the cathode. In this electrolysis system, the degradation of organic pollutants is realized by the simultaneous oxidation of active anode and oxidant species electrogenerated on the cathode. It is expected to increase notably the degradation rate of organic pollutants without adding metal catalyst.Electrochemical oxidation of methyl orange wastewater was studied using Ti/IrO₂/RuO₂ anode and a self-made carbon/polytetrafluoroethylene （C/PTFE） O₂-fed cathode in the divided cell with a terylene diaphragm. The result indicated that appropriate aeration rate was favorable of improving the methyl orange removal efficiency. The decolorizing efficiency of methyl orange in the divided cell increased with increasing in current density, and it was slightly affected by initial pH. When the current density was 46 mA/cm² and aeration rate was 30 mL/s, after 60 min, the color removal efficiency was 100%, the average COD removal efficiency was 80%.Chlorophenol pollutants, having high toxicity biorefractory, bioaccumulation and carcinogenic potential are widely found in the environment and are significant contaminants at many sites selected for cleanup on the USEPA top priority toxic pollutants list. There is need to treat such contaminants in concerning of environmental protection. In present work, we present a detailed study on the degradation of chlorophenol pollutants in the diaphragm cell with an organic synthesized diaphragm, a Ti/IrO₂/RuO₂ anode, and home-made gas-diffusion cathodes, and developing an effective and friendly method to treat chlorophenol pollutants by using a combination process of reduction and oxidation. In the cathodic compartment, the chlorine atoms of chlorophenol pollutants are removed from the aromatic structure and chlorophenol pollutants are reduced to non-chlorinated intermediates. Then, the non-chlorinated intermediates are oxidized and degraded in the anodic compartment and the cathodic compartment.Pd/C catalyst used for the Pd/C gas diffusion cathodes is prepared by hydrogen reduction method and formaldehyde reduction method, and characterized by X-ray diffraction （XRD）, transmission electrode microcopy （TEM）, X-ray photoelectron spectroscopy （XPS）, and cyclic voltammetry （CV） techniques. The electrochemical degradation of chlorophenol pollutants （4-chlorophenol, 2,4-dichlorophenol, and sodium pentachlorophate） is investigated in the diaphragm electrolysis system through three kinds of gas types, using three different kinds of gas diffusion cathode. The results indicated that the self-made Pd/C gas diffusion cathode can not only reductively dechlorinate chlorophenol pollutants by aerating hydrogen gas, but also accelerate the two-electron reduction of O₂ to hydrogen peroxide （H₂O₂） by aerating air. Furthermore, the type of aeration, that is, first air, then hydrogen, is in favor of improving chlorophenol pollutants removal efficiency. Therefore, both the removal efficiency and the dechlorination degree of chlorophenol pollutants reach about 100% after 100 min.By high-performance liquid chromatography （HPLC）, the main intermediates of 2,4-dichlorophenol dechlorination in the cathodic compartment are determined as 4-chlorophenol and 2-chlorophenol, which further dechlorinate to phenol. Benzoquinone is the first product formed from the oxidation of phenol. The further oxidation of benzoquinone, after ring opening, leads to the formation of aliphatic carboxylic acids such as maleic acid, fumaric acid and oxalic acid. A reaction scheme involving all these intermediates is proposed.Therefore, it is feasible to degrade chlorophenol pollutants by electrochemical reduction to phenol, which is further degraded on the cathode and anode by electrochemical oxidation in the diaphragm electrolysis.更多还原